As more and more data are created and communicated through the networks, it has become quite preferred, if not essential, for corporations to address data storage issues. To store massive amount of data, racks of hot-swappable hard disk drives (“HDD”) have been developed, commonly called a storage chassis. Referring to FIG. 1, a storage chassis typically has a host of hot-swappable HDDs 10, which is connected to a backplane with expanders (12) through a HDD connector 39. The backplane 12 is connected to the host bus adapter 14 (“HBA”) through an SAS HBA connector 31. The connection methodology is commonly referred to as an Serial Attached SCSI (“SAS”) connection. FIG. 1 is now further described as follows.
The backplane 12, such as the one shown in FIG. 1, typically refers to a circuit board containing sockets into which other circuit boards or devices can be plugged in. In the data storage field, a pluggable device refers to a HDD. Backplanes are often described as being either active or passive. Active backplanes contain, in addition to the sockets, logical circuitry that performs computing functionality. In contrast, passive backplanes contain almost no computing circuitry.
The SAS connection, such as the one shown in FIG. 1, is a newer generation serial communications protocol for devices designed to allow for much higher speed data transfers. SAS uses serial transfer, instead of the parallel transfer found in traditional SCSI devices. SAS still uses SCSI commands for interacting with SAS devices.
Expanders on the backplane 12 refer to active components in the SAS connection. Expanders are the key to Serial Attached SCSI's remarkable scalability. Each of these low-cost switches enables up to 128 point-to-point connections to be made off a single HBA/enclosure, and a total of 16,384 SAS devices can be aggregated while preserving performance and reliability.
In today's market, delivering high-density, scalable and reliable storage solutions to market quickly is a necessary goal for storage solution designers, original equipment manufacturers (OEMs), system integrators. If achieved, they can keep the competitive edge needed for continued success. The aforementioned SAS connection has defined a device called an “expander,” which allows thousands of combinations of storage expansion to achieve the needs for IT professional on storage availability, flexibility, scalability, and performance. However, the conventional backplane connection requires IT engineers to create many more complex storage backplanes that may be dedicated to only a single solution.
The pre-dominant high availability physical interconnect technology between the hot-swappable HDDs and storage HBAs rely on transmission of data streams through a piece of physical PCB board (Backplane Board). The SAS expander is laid out on the backplane to provide multiple functionality enabled by the SAS connection.
With the conventional method, all expanders 20 are embedded on the backplane board 12, as shown in FIG. 2. The conventional method forces designers to design backplanes with more than twenty PCB layers, which tend to generate unnecessary signal skew, crosstalk and DC interference, and block airflow, etc. Also, such design restricts failed over and device addressability as well as configuration flexibility, and stands as a barrier to throughput performance, storage scalability, system flexibility and availability.
Further, because of the size of the expander footprint and/or other IC components form factor, IT engineers have to carefully confront the trade-offs between reliability, scalability, performance and availability of the application requirements. This inflexibility on the conventional backplane design forced designers to implement separate and distinct systems for each type of solution. Such approach translates to high costs of additional backplane design, additional layers, prototypes, troubleshoot, manufacture and support. A single failure of individual components in a backplane requires a replacement of a new backplane, causing single points of failure to block access to the system. This results in high support cost and increased total cost of ownership.
Conventional Design of SAS Backplane.
To illustrate, a conventional method of designing an SAS backplane is described. The SAS backplane consists of both active and passive components in the same backplane. The active part includes the expanders that perform computing functions to enable multiple HDD support and other SAS topology. The function of the SAS backplane is to connect the hot-swappable HDD to the HBA that can enable SAS topology and drive expansion. The conventional SAS backplane consists of:
a. HDD hot-pluggable connector receptacles, which are used to connect to the hot-swappable HDD, and enable the HDD to be replaceable without turning off the system. Because of the large footprint of an SAS expander and/or other active/passive components, the receptacles can only be assembled with surface mounting technology (SMT), which causes structural weakness when compared with through-hole mounting technology.
b. Power connectors, which provide power to hot-swappable HDD, all active and passive components of the backplane. The conventional backplane may require many power connectors on the backplane, and require extra current and voltage stabilizers to be presented. Thus, it results in high cost and complex and unstable circuitry.
c. Other discrete components, such as power MOSFET, resistors, capacitors, diodes, isolators, sensors, transistors, transformer, which provide various functions on the backplane. The complicated circuitry of the conventional SAS backplane forces designers to layout many layers of trace, thus resulting in longer design time, higher design and manufacturer's difficulty and cost.
d. Traditional backplanes also include hot-swappable HDD status LEDs to provide indication to the user HDD status through the Serial General Purpose Input/Output.
e. SAS expanders, the activity component of the backplane, which enable scalability, flexibility, availability and performance of the SAS storage system. The SAS expander chip enables single cable connection from the HBA to support up to 128 devices per cable. The expanders comply with the SAS standard which includes the proven SCSI command set, while allowing for point-to-point connection, increased device bandwidth, higher availability with dual-ported drives, enhanced reliability, and greater flexibility. However, the SAS expander chip has a large foot print, thus requiring a large area of placing space and complex circuitry, making it a very tough task to design.
f. A conventional backplane contains board-to-cable connectors that are used to connect the backplane to the HBAs. The SAS technology enables a dual-ported host that enhances better performance, reliability and greater flexibility. However, that will also require more backplane-to-host (HBA) connectors, making the limited conventional backplane space dense.
Therefore, it is desirable to avoid having to replace the whole backplane due a single or even minor failure.
It is also desirable to reduce the cost of support, as well as cost of ownership.